In vehicles having an internal combustion engine with an electronic returnless fuel system (ERFS), fuel priming methods may be used for fuel delivery during an engine start to achieve a desired air-fuel ratio (A/F ratio). Two such methods include: 1) open-loop fuel pump priming to a predetermined, fixed fuel pump input voltage in combination with a closed-loop fuel pump after priming/initialization, and 2) closed-loop fuel pump priming to a specified fuel pressure target value.
The priming method involving an open-loop fuel pump priming an engine to fixed fuel pump input voltage may be effective in achieving rapid fuel pressure rise times. In this method, the fixed fuel pump input voltage may be maximized during priming. Despite this maximization, the inventors herein have recognized a number of potential issues with such a control method.
One issue of this open-loop system priming to a fixed input voltage is that the resultant fuel pressure at the end of open-loop operation may be dependant on the available fuel pump electrical input power. Further, this end fuel pressure may be independent of a desired target fuel pressure. Thus, the fuel pressure may overshoot the target fuel pressure during priming. Additionally, this method may promote the closure of the check valve in the fuel delivery line. As a result, there may be disrupted feedback from the fuel pump to the injection pressure sensor. This may allow fuel pressure to build incrementally to the limit of the pressure relief valve under subsequent ignition key cycles during engine priming.
An alternative control method utilizing a closed-loop fuel pump controlled to a specified fuel pressure target value may overcome some of the disadvantages of the above-described open-loop system. The specific target pressure of a closed-loop may be a function of one or more input factors, including, but not limited to, engine temperature, fuel temperature, or barometric pressure. This method may be effective in enabling fuel pressure to be controlled to the target fuel pressure.
However, the inventors herein have recognized a number of potential issues with such a closed-loop fuel priming control method. For example, when using control gain values that give a desired fuel pressure control during running engine operation, these values may result in undesirable, slow fuel pressure rise times during priming. Likewise, the gain values that can provide fast pressure rise times during priming may result in fuel pressure variation during running engine operation.
At least some of the disadvantages of both of the above described fuel system priming methods may be overcome by a method for priming a fuel injected internal combustion engine with a returnless fuel system having a check valve. The method comprises initiating a fuel pump with a command signal; after said initiation, adjusting said command signal as a sensed fuel pressure varies to achieve a fuel pressure; and holding said command signal for a hold period after achieving said fuel pressure. In one example, the initiating command signal may be an open-loop signal held substantially constant for a first period.
Thus, in one example, an initial open-loop control can be used that is later modified by information for sensed pressure. In this way, advantages of both open and closed-loop control may be achieved, while reducing at least some of the above identified issues. For example, by using a holding period, it may be possible to maintain a substantially zero pressure differential across the check valve in the fuel system while the system is deadheaded, thereby reducing the potential for disrupting the ability for feedback. Further, such operation may provide for increased responsiveness once fuel injection begins. In this way, it may be possible to obtain accurate initial priming of the fuel system, while also compensating for various external effects.
In another embodiment, at least some of the disadvantages of both of the above described fuel system priming methods may be overcome by a method for priming a fuel injected internal combustion engine with a returnless fuel system, comprising: calculating a target fuel pressure based on operating conditions; initiating a fuel pump using an open-loop control; increasing fuel pressure to a target pressure using a closed-loop control; maintaining a command fuel pump output value at the targeted fuel pressure; anticipating a first fuel injection; and adjusting the command fuel pump output to a level necessary to satisfy flowing fuel injection requirements prior to fuel injection.
Thus, the inventors herein have recognized that a priming system utilizing both an open-loop control and a closed-loop control may enhance the robustness of initial fuel delivery during an engine start and limit fuel delivery variability by minimizing fuel pressure rise time to a targeted fuel pressure. Note that both the open-loop and closed-loop controls may include calculations based on engine operating conditions. In this method, the operating conditions upon which the target fuel pressure may be calculated may include fuel temperature, barometric pressure, and/or engine temperature but may be independent of the fuel pump electrical input power and the number of ignition key cycles.
Further, the method may use a delay mechanism in order to provide time for the fuel pressure to rise to the target pressure. The mechanism may be any mechanism capable of being activated during or after the open-loop control initiates the fuel pump. One such mechanism may be a passive anti-theft security system (PATS). PATS may be initiated immediately after the intelligent open-loop fuel pump command is directed to the fuel pump, or during the initial pressure rise of the open-loop fuel pump operation. Therefore, the fuel pump command signal may be sent to the fuel pump for an amount of time indirectly controlled by the duration of time required to complete the PATS subroutine. If PATS is not used, a timer could be substituted to act in a similar way as a delay mechanism to provide the time necessary for the fuel pressure to rise to the target pressure.
In still another example, a method for priming a fuel injected internal combustion engine with a returnless fuel system having a check valve, the method comprising: initiating a fuel pump with a command signal; after said initiation, achieving a fuel pressure with a command signal at a first level; and before a first fuel injection event, increasing said command signal to a second level higher than said first level to reduce a decreasing of fuel pressure caused by commencement of said first fuel injection event.
By increasing fuel pressure in anticipation of a first injection and reducing a drop in fuel pressure, it may be possible to obtain more consistent and accurate fuel control during starting, thereby reducing emissions.
Example advantages that may be achieved by various example embodiments disclosed herein may include the ability to control fuel delivery during an engine start, so as to limit fuel delivery variability as well as provide robust fuel delivery at an engine start.